Although moves in the Dow Jones industrial average and S&P look fairly innocuous, Jim Cramer said something significant happened in the market on Thursday, though it was not readily apparent.

"Today, momentum stocks came roaring back and safety was abandoned," Cramer said. "But why? What's changed, at least for now?"

To get a better handle on the market and what's behind the surprising price action, the "Mad Money" host says it's critical to examine what triggered the decline in the first place.

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"Internet and 'software as service' stocks first stalled in February, when Salesforce made a dramatic U-turn after reporting a picture-perfect quarter," Cramer said, noting that was the beginning.

Largely, money pros feared the price action in Salesforce was a sign that so-called momentum stocks had simply gone too high, even for growth investors who are used to significantly inflated valuations.

From that time forward, momentum stocks followed a pattern.

"As those companies reported earnings, they showed really great sales," Cramer said. "On the news, shares popped in after-hours trading but then would turn down swiftly the next day. Again, this process started with Salesforce at the end of February and continued right through yesterday."

However, that pattern finally broke when Yelp, another momentum stock, started down after earnings and then U-turned back up.

When Yelp broke the mold, Cramer said, buyers flocked back to the entire group.

Behind the scenes, Cramer said another force has come into play. "In the last 48 hours, three young companies with no real history of making money postponed their IPOs."

The delayed IPOs combined with the price action in Yelp was interpreted by investors as a kind of green light to again buy these momentum stocks.

However, just because momentum stocks finally rallied on Thursday, doesn't mean Cramer would dive into this pool.

"I want to be clear about this. I want you to understand why momentum stocks are bouncing," Cramer said. "But, this market's become amazingly fickle. What's loved today could be hated tomorrow. I would not run from safety nor would I run toward momentum. I believe in diversification, and my charitable trust owns a smattering of both."